Typically, mobile phone coverage is provided by transmitting the RF signals from basestations. Users' handsets communicate with the network by transmitting signals back to the basestation. A problem faced by mobile phone operators is that certain locations receive a poor quality of reception or, in some cases, no reception at all. These areas of poor reception are generally caused by the RF signals being blocked by natural or other obstacles. Examples of areas of poor reception are valleys or other areas in which the natural landscape prevents the penetration of the signals, built up areas in which buildings block the RF signals or within buildings where the general building layout prevent the mobile signals from reaching all parts of the building.
One solution to improving the coverage in areas of poor reception is repeaters. Repeaters are placed around areas of poor coverage but in locations where RF signals can be received. Repeaters operate by receiving RF signals from basestations, amplifying the signal and re-transmitting the signal into the area of poor coverage. They also receive signals from handsets in the vicinity of the repeater, amplify these and retransmit them to the basestation. Although repeaters improve the level of coverage in certain areas their successful operation is entirely reliant on their ability to receive the RF signal from the basestation. Another problem is that they retransmit the signal in vicinity in which it was received and so, although they boost the signal strength, in many cases they cannot fully penetrate areas of poor coverage. A further problem is that feedback between the receiver and the transmitter can cause operational problems and so careful setup of the repeaters is required. These factors increase the installation costs and reduce the application for repeaters to provide enhanced coverage in many areas.
In a second known solution, RF mobile phone signals are inserted directly into existing cables, for example television cables, within buildings or, on a wider scale, in underground distribution cabling. The RF signals are received from either repeaters in good coverage locations or dedicated basestations and are input into the cable and passed through the cable to transmitters positioned in areas of poor coverage. A problem faced by such systems is that existing cabling includes components, for example amplifiers, which only allow the passage of signals which are within particular frequency ranges. Generally, the frequency of RF mobile phone signals falls outside the frequency range of such amplifiers and so would be filtered by the amplifier which results in data loss. In order to avoid the loss of the RF signals in this situation, the RF signal must bypass the amplifier by being filtered out of the cable before it reaches the amplifier and then reinserted after the amplifier. In practice, in order to avoid RF signal loss, the cable must be accessed at the position of the amplifier and a bypass cable attached on either side of the amplifier which retrieves the RF signal and reinserts it after the amplifier. The bypassing of every amplifier or other potentially filtering component in a pre-installed cable makes installation of bypass components inconvenient and is impractical.
Accordingly, it would be beneficial to carry an RF signal into an area of poor coverage using pre-installed cabling. However, the requirement of physically inserting filters and bypass components around each amplifier or device which would filter the RF signal is impractical for large scale implementation.